SONG-TYPE SHARING IN SONG SPARROWS - IMPLICATIONS FOR REPERTOIRE FUNCTION AND SONG LEARNING

One hypothesis for the function of song repertoires is that males lear n multiple song types so that they may share songs with neighbors, all owing them to match during territorial interactions. In at least one s ong sparrow population, in Washington, territorial males share a high proportion of song types with their neighbors and use these shared son gs in matching. We recorded song sparrows in Pennsylvania and quantifi ed sharing of whole songs and song segments. We found that song sharin g is an order of magnitude less common in the Pennsylvania population. We found sharing of song segments to be significantly more common tha n the sharing of whole songs in three of the five fields we examined, while we found no significant differences between whole and partial so ng sharing in the remaining two fields. Finally, we found no evidence that sharing is greater between birds in the same field compared to bi rds in different fields. Taken with the data from Washington song spar rows, these results provide evidence for intraspecific geographic vari ation in the organization of song repertoires, and suggest that song s haring has not been a strong selective force in the evolution of song repertoires in song sparrows as a species. Furthermore, Washington and Pennsylvania song sparrows differ in how they learn song, in that Was hington birds copy whole songs, while Pennsylvania birds appear to cop y and recombine song segments, as has been found in laboratory studies of song learning. Thus both song learning and the function of song re pertoires differ between populations of song sparrows. Such intraspeci fic geographic variation offers a unique opportunity to explore the ec ological and historical factors which have influenced the evolution of song.